High Thermoelectric Power Factor of High-Mobility 2D Electron Gas

Thermoelectric conversion is an energy harvesting technology that directly converts waste heat from various sources into electricity by the Seebeck effect of thermoelectric materials with a large thermopower (S), high electrical conductivity (σ), and low thermal conductivity (κ). State-of-the-art nanostructuring techniques that significantly reduce κ have realized high-performance thermoelectric materials with a figure of merit (ZT = S²∙σ∙T∙κ^-1) between 1.5 and 2. Although the power factor (PF = S²∙σ) must also be enhanced to further improve ZT, the maximum PF remains near 1.5-4 mW m^-1 K^-2 due to the well-known trade-off relationship between S and σ. At a maximized PF, σ is much lower than the ideal value since impurity doping suppresses the carrier mobility. A metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) structure on an AlGaN/GaN heterostructure is prepared. Applying a gate electric field to the MOS-HEMT simultaneously modulates S and σ of the high-mobility electron gas from -490 µV K^-1 and ≈10^-1 S cm^-1 to -90 µV K^-1 and ≈10⁴ S cm^-1, while maintaining a high carrier mobility (≈1500 cm² V^-1 s^-1). The maximized PF of the high-mobility electron gas is ≈9 mW m^-1 K^-2, which is a two- to sixfold increase compared to state-of-the-art practical thermoelectric materials.